The development of boundaries between cells and tissues is a critical feature of pattern formation and these same boundaries must be maintained during later adult homeostasis. The mechanisms of boundary establishment and implementation are thus of fundamental biological significance and have profound implications for understanding birth defects as well as cancers, in which boundary constraints are lost, and regeneration, in which boundaries must be formed anew. The goal of this project is to understand the genetic and cellular mechanisms underlying an especially tractable example of boundaries in a post-embryonic vertebrate, the adult pigment stripes of zebrafish. Previous efforts demonstrated that interactions between different classes of pigment cells are essential for stripe development and maintenance, though the particular genes and cell behaviors involved have been elusive. In Aim 1, innovative hypotheses to explain the specification of stripes and their dynamic reiteration will be tested using mutational and transgenic approaches, cell transplantation and analyses of a naturally occurring pattern variant. In Aim 2, efforts will focus on mechanisms of subsequent pat- tern implementation, testing roles for specific cellular behaviors and signaling pathways in refining a striped pattern once it has been established, and how these factors have changed to generate a pattern that lacks stripes. These studies will provide valuable new insights into pigment cell boundary formation, with relevance to human health and development, and promise to shed light on the logic of boundary forming mechanisms more generally.